1. Field of the Invention
The present invention relates to position data acquisition and, more particularly, to a device and method to be used as part of position-sensing apparatuses.
2. Description of the Prior Art
In the field of information sensing, machine vision technologies provide valuable information about the environment and about specific objects of interest through close inspection. Known 3-D data acquisition systems have been provided using 3-D sensors based on the active triangulation principle. In such systems, a specific known and fixed pattern of illumination (i.e., structured illumination) is projected from a light source (e.g., laser) on an object to be measured, and the intersection of that emitted pattern is observed from a known and fixed oblique angle by a digital camera, having photodetection means such as a charged coupled device (CCD) array, whereby the position of the illuminated points on the object translate to positions on the camera array, such that the position of the illuminated points on the object can be computed trigonometrically.
Triangulation uses a functional relation carried out by the imaging system between the position of the luminous spot on the observed surface and the position of the image of this spot measured by the CCD array. Due to this functional relation, the determination of the image position allows the unambiguous determination of the position in the 3-D space of the surface portion intercepted by the illumination beam.
For instance, one of these systems is referred to as a laser profilometer, wherein a laser is used as the light source for illumination. Such profilometers analyze deformations of a laser line on an object to evaluate, for instance, the depth (Z-axis) as well as the horizontal position (X-axis) of the object. Generally, the translation of either one of the profilometer and the object to be scanned by way of a translation mechanism allows the missing vertical position (Y-axis) to be obtained by knowing the rate of displacement between the object and the profilometer. The points of the emitted pattern observed by the digital camera are positioned with respect to the digital camera by calculations involving the focal length, the position of the transmitted light pattern on the CCD array, the distance and angle between the digital camera and the laser
Among the design limitations affecting the speed of off-the-shelf profilometers are the acquisition speed, in images per second, of the digital camera, and the processing capacity of the data processing system in extracting the laser profile and computing the positions thereof, considering the four above-mentioned values required for carrying out the calculations of the positions. Because of these limitations, the off-the-shelf profilometers perform maximum acquisition speeds ranging between 1,000 and 2,000 profiles per second.